Vitamin C Serum Formulation: Stability and Ingredient Compatibility

Based on the formula you provided and the staff's response:

1. Regarding the oil emulsifier: The ingredient list you provided includes a line "สารประสานน้ำมัน ...%" but does not specify which ingredient it is or its percentage. The staff suggested using Satin Cream Maker (ID 247) or Pro Polymer (ID 234) to help emulsify or thicken the formula. Your formula appears to be primarily water-based, so these ingredients would likely function as thickeners or stabilizers to create a serum texture, or emulsify a small oil phase if one is intended but not listed.

2. Regarding formula improvement: The staff correctly pointed out the main challenge with this formula: the instability of L-ascorbic acid (ID 133). L-ascorbic acid is prone to degradation, especially in the presence of ingredients that raise the pH, such as Triethanolamine (ID 139) which is included in your formula.

To improve the stability and effectiveness of your Vitamin C serum, consider the following:

• Adjust pH: L-ascorbic acid is most stable and effective at a low pH (around 2.5-3.5). The Triethanolamine in your formula will raise the pH, accelerating degradation. You would need to adjust the pH down using an acid (like Ferulic Acid or Citric Acid, carefully) or use a different pH adjuster, but achieving and maintaining the correct low pH can be tricky and may cause skin irritation.
• Use a more stable Vitamin C derivative: Instead of L-ascorbic acid, consider using more stable forms of Vitamin C like Sodium Ascorbyl Phosphate, Magnesium Ascorbyl Phosphate, Ascorbyl Glucoside, or Tetrahexyldecyl Ascorbate. These are less pH-dependent and easier to formulate.
• Simplify the formula: A complex formula with many active ingredients can increase the risk of interactions and instability.
• Follow a proven formula: As the staff recommended, using a tested and stable formulation like the Vitamin C E Ferulic Kit (ID 70) is often a better approach for beginners, as these kits are designed for stability.

In summary, the specific oil emulsifier is missing from your list, but Satin Cream Maker or Pro Polymer were suggested. The primary improvement needed is to address the stability of L-ascorbic acid, likely by adjusting pH, using a different Vitamin C form, or simplifying the formula, or using a stable kit.